IMMUNITY AND SUSCEPTIBILITY. 565 



producing these substances in the serum of the immune animal, cytotoxins 

 for spermatozoa of the same species are also produced, showing that these 

 cells have some chemical substances in common. 



Cytotoxins are similar to bacteriolysins and hemolysins, they consist 

 of amboceptors which are activated by the complement which is normally 

 present in the serum or other body fluids. 



THE OPSONINS AND PHAGOCYTOSIS. It was shown a number of years 

 ago that certain types of leucocytes and other body cells were capable of in- 

 gesting bacteria and other plant and animal cells. The mechanism of 

 this process was not known until Wright and Douglas demonstrated 

 certain substances in the blood serum and other body fluids which have the 

 power of rendering the bacteria susceptible to phagocytosis. These sub- 

 stances are known as opsonins (Gr. I prepare food for). It has been shown 

 that the phenomena of the phagocytosis depends almost wholly on these 

 specific opsonins. Leucocytes which have been washed free from all serum 

 will not take up bacteria except a few in rare instances. Bacteria which 

 have been placed in contact with blood serum or other body fluids may be 

 thoroughly washed, and when they are placed in contact with the leuco- 

 cytes, they will be taken up. The opsonin acts chemically upon certain sub- 

 stances within the bacteria, and, so to speak, sensitizes them. Opsonins 

 for the various bacteria are present in many normal sera. They may 

 be produced in animals not containing them by the process of immunization 

 with various antigenous microorganisms. Opsonins are destroyed at 

 about 60 for thirty minutes, but there is some variation among them. 

 When kept at o these opsonins will remain active for several days, but 

 at a temperature of the body, 37, after the serum has been withdrawn, 

 they rapidly deteriorate. Many opsonins have the features of agglu- 

 tinins and precipitins, although they bear some points of resemblance to 

 antitoxins and complements. They possess two groups, a haptophile 

 group with which they combine with the bacteria and the functional group 

 which really sensitizes the microorganism and makes it phagocytable. 



It has been shown that the opsonins may be increased in the serum 

 of the normal or infected individual by the injection of heated (6o.) 

 cultures of the specific etiological microorganisms. Such substances are 

 called opsonogens or vaccines. They have been used to a great extent in 

 the treatment of the various pus infections due to the staphylococci and 

 also in tuberculosis and pneumonia. It is supposed that the opsonins are 

 produced in the subcutaneous tissues and in the muscles. 



